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Iodine liberation from KI with ultrasound
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From "Sonochemistry and Sonoluminescence",
Edited by Lawerence J. Mason, Jacques L. Reisse, and Kenneth S. Suslick (1999),
Library of Congress # QD 801 S66 1999
Page 276
"5.2 Radical Reactions - Hetrolytic Fission
In classical organic chemistry covalent bonds can be broken to form radicals
useing heat or light. Hetrolytic fission can also be acheived through
sonochemistry and such reactions are typified by the sonochemical degradation
of hydrocarbons. ...
The sonochemical reaction most frequently quoted for radical production is the
sonolysis of water in the cavitation bubble a simplified scheme for which is
shown below. The intial homolytic fission of the H-O bond is followed by a whole
series of other radical reactions.
H-O-H ---> H* + HO*
H* + O2 --> HO2*
HO2* + HO2* --> H2O2 + O2
HO* + HO* --> H2O2
... A whole range of reations can take place subsequently one of which is the
production of H2O2, hydrogen peroxide a common oxidant. It is the decomposition
of water from which are derived the most frequently used forms of chemical
dosimetry for sonochemistry. These are (a) the oxidation of iodide ion to iodine
and (b) methods based on the trapping of the free radical species HO* as they
emerge from the bubble. ...
Iodine dosimetry is based upon the oxidation of iodide ion by the hydrogen
peroxide generated by sonolysis of water (Equation 3).
H2O2 + 2 KI + 2 H(+) ---> I2 + 2 H2O Equation 3
...
The yield of iodine is usually quite small when the reaction is carried out
useing pure aqueous potassium iodide solution. In order to increase the iodine
yield, i.e. the sensitivity of the reaction, a saturated aqueous solution of
carbon tetrachloride is sometimes used in place of water as the solvent
(Weissker's solution). When this solution is sonicated the normal oxidation
process occurs together with generation of chlorine from the hetrolytic
breakdown of CCl4 in the bubble (Equation 4). The chlorine itself then
acts as an oxidizing agent for the iodide ion (Equation 5).
CCl4 + H2O --> Cl2 + CO2 + 2 HCl Equation 4
2 I(-) + Cl2 --> I2 + 2 Cl(-) Equation 5
There is also a possiblity of using CHCl3 (Chloroform) which might not have as
perfect result but the liberation iodine will still be there.
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